Electrode unit, electrolytic cell comprising electrode unit, electrolytic device and method of manufacturing electrode of electrode unit

ABSTRACT

According to one embodiment, an electrode unit of an electrolytic device includes a first electrode including a first surface, a second surface located on a side opposite to the first surface, and a plurality of through-holes opening on the first surface and the second surface, a second electrode opposed to the first surface of the first electrode, and a porous membrane containing an inorganic oxide and provided on the first surface of the first electrode to cover the first surface and the through-holes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of PCT Application No. PCT/JP2015/056388, filed Mar. 4, 2015 and based upon and claiming the benefit of priority from Japanese Patent Application No. 2014-191992, filed Sep. 19, 2014, the entire contents of all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electrode unit, an electrolytic cell comprising an electrode unit, an electrolytic device and a method of manufacturing an electrode for an electrode unit.

BACKGROUND

In recent years, an electrolytic device for electrolyzing water and producing an electrolyzed aqueous solution which has various functions, such as an ionized alkaline solution, an ozone solution or aqueous hypochlorous acid has been provided. This electrolytic device comprises an electrolytic cell, and an electrode unit provided in the electrolytic cell.

For example, an electrolytic device comprising a three-chamber electrolytic cell is proposed. The electrolytic cell is divided into three chambers, specifically, an intermediate chamber and anode and cathode chambers located on both sides of the intermediate chamber, by cation- and anion-exchange membranes included in an electrode unit. The electrode unit comprises an anode and a cathode. The anode and the cathode of the electrode unit are provided in the anode and cathode chambers, respectively. As the electrodes, an electrode having a porous configuration is used. A large number of through-holes are formed on the matrix made of a metal plate by applying expanding, etching or punching.

In this type of electrolytic device, for example, a salt water is supplied to the intermediate chamber, and water is supplied to the anode and cathode chambers. The salt water in the intermediate chamber is electrolyzed by the cathode and the anode. In this manner, aqueous hypochlorous acid is produced from the gaseous chlorine produced by the anode. Aqueous sodium hydroxide is produced in the cathode chamber. The produced aqueous hypochlorous acid is used as a disinfectant. The aqueous sodium hydroxide is used as a cleaning solution.

In the three-chamber electrolytic cell, the anion-exchange membrane is degraded easily by chlorine or hypochlorous acid. When an electrode having a porous configuration adheres tightly to an ion-exchange membrane (electrolyte membrane), stress is easily concentrated on the edge portion of the pores of the electrode. Thus, a diaphragm formed of, for example, a thin electrolyte membrane which is weak mechanically, deteriorates easily. In consideration of this factor, the following technique is suggested. Nonwoven fabric having overlaps or slits is inserted between an electrode having a porous configuration and an electrolyte membrane to reduce the degradation of the electrode by chlorine.

An electrode unit in which a porous inorganic oxide membrane is formed in a flat valve electrode by sol-gel is known.

However, the electrolytic device having the above structure cannot avoid degradation of the electrode unit when operated for a very long time.

Embodiments described herein aim to provide an electrode unit, an electrolytic device and a method of manufacturing an electrode for an electrode unit, enabling the electrolytic performance to be maintained for a long time and allowing long-life operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an electrolytic device according to a first embodiment.

FIG. 2 is an exploded perspective view showing an electrode unit of the electrolytic device according to the first embodiment.

FIG. 3A is a cross-sectional view in which an electrode and a porous membrane of the electrode unit are enlarged.

FIG. 3B is a cross-sectional view in which the electrode and the porous membrane of the electrode unit are enlarged.

FIG. 3C is a cross-sectional view schematically showing the porous membrane formed by a multilayer film.

FIG. 3D is a cross-sectional view schematically showing the porous membrane formed by an inorganic oxide film having irregular pores in a plane or in a three-dimensional manner.

FIG. 4 is a cross-sectional view showing the electrode unit according to a first modification example.

FIG. 5 is a cross-sectional view showing the electrode and the porous membrane of the electrode unit according to a second modification example.

FIG. 6 is a perspective view showing an electrolytic device according to a second embodiment.

FIG. 7 is an exploded perspective view showing an electrode unit of the electrolytic device according to the second embodiment.

FIG. 8 is a cross-sectional view showing the electrode unit according to the second embodiment.

FIG. 9 is a cross-sectional view showing a process for manufacturing an electrode for the electrode unit according to the second embodiment.

FIG. 10 is a cross-sectional view showing a process for manufacturing the electrode and a porous membrane.

FIG. 11 is a cross-sectional view showing the electrode unit according to a third modification example.

FIG. 12 is a cross-sectional view of an electrolytic device according to a third embodiment.

FIG. 13 is a cross-sectional view of an electrolytic device according to a fourth embodiment.

FIG. 14 is a cross-sectional view showing an electrode unit according to a fourth modification example.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference to drawings. In general, according to one embodiment, an electrolytic device comprises an electrode unit. The electrode unit comprises: a first electrode comprising a first surface, a second surface located on a side opposite to the first surface, and a plurality of through-holes opening on the first surface and the second surface; a second electrode opposed to the first surface of the first electrode; and a porous membrane containing inorganic oxide, provided on the first surface of the first electrode to cover the first surface and the through-holes.

Structures common in embodiments are denoted by the same reference numbers or symbols. Overlapping explanations are omitted. Each figure is an exemplary diagram of an embodiment to prompt understanding of the embodiment. The shapes, dimensions or ratios in the drawings may differ from those of the actual device. However, they may be appropriately changed in consideration of the explanation below and known art. For example, the drawings show that electrodes are provided on a plane surface. However, the electrodes may be bent or cylindrical in accordance with the shape of the electrode unit.

First Embodiment

FIG. 1 schematically shows an electrolytic device according to a first embodiment. An electrolytic device 10 comprises, for example, a two-chamber electrolytic cell 11 comprising an electrode unit 12.

The electrolytic cell 11 is formed in the shape of a flat and rectangular box. The electrolytic cell 11 is divided into two chambers, specifically, an anode chamber 16 and a cathode chamber 18, by a diving wall 14 and the electrode unit 12.

The electrode unit 12 comprises a first electrode (anode) 20 located in the anode chamber 16, a second electrode (a counterelectrode, a cathode) 22 located in the cathode chamber 18, and a porous membrane 24 provided between the first and second electrodes.

The electrolytic device 10 comprises a power supply 30 which applies voltage to the first and second electrodes 20 and 22 of the electrode unit 12, ammeter 32, a voltmeter 34 and a control device 36 which controls these elements. A flow channel for liquid may be provided in the anode chamber 16 and the cathode chamber 18. For example, a pipe or a pump for supplying liquid from outside or discharging liquid may be connected to the anode chamber 16 and the cathode chamber 18. A porous spacer may be provided between the electrode unit 12 and the anode chamber 16 or the cathode chamber 18.

Now, this specification explains the electrode unit 12 in detail. FIG. 2 is an exploded perspective view of the electrode unit.

As shown in FIG. 1 and FIG. 2, the first electrode 20 has a porous configuration in which a large number of through-holes 13 are formed on a matrix 21 made of, for example, a rectangular metal plate. The plate-like matrix 21 comprises a first surface 21 a, and a second surface 21 b facing and substantially parallel to the first surface 21 a. The interval between the first surface 21 a and the second surface 21 b, in other words, the thickness of the plate, is defined as T1. The first surface 21 a faces the porous membrane 24. The second surface 21 b faces the anode chamber 16.

A large number of through-holes 13 are formed on the whole surface of the first electrode 20. The through-holes 13 open on the first surface 21 a and the second surface 21 b. In the present embodiment, each through-hole 13 is formed by a tapered wall surface or a curved wall surface such that the opening dimension on the first surface 21 a side is greater than that on the second surface 21 b side. Each through-hole 13 may take a variety of forms such as a square, a rectangle, a rhomboid, a circle or an ellipse. The vertexes of a square, a rectangle or a rhomboid may be rounded. The through-holes 13 need not be aligned regularly and may be arranged randomly.

For the matrix 21 of the first electrode 20, valve metal such as titanium, chromium, aluminum or an alloy thereof, or conductive metal may be used. Of these materials, titanium is preferable. An electrocatalyst (catalytic layer) is preferably formed on the first and second surfaces 21 a and 21 b of the first electrode 20 depending on the electrolytic reaction. In the case of the anode, as the catalyst, a noble metal catalyst such as platinum or an oxide catalyst such as iridium oxide is preferably used. The amount of electrocatalyst per unit area on one surface of the first electrode may differ from that on the other surface of the first electrode. In this manner, for example, a side reaction may be prevented. The surface roughness of the matrix 21 is preferably 0.01 to 3 μm. When the surface roughness is equal to or less than 0.01 μm, the actual surface area of the electrode is reduced. When the surface roughness is equal to or greater than 3 μm, the stress applied to the porous membrane is easily concentrated on the convex portion of the electrode. The surface roughness of the matrix 21 is more preferably 0.02 to 2 μm, and is further preferably 0.03 to 1 μm.

As shown in FIG. 1 and FIG. 2, in the present embodiment, the second electrode (counterelectrode) 22 is structured in the same manner as the first electrode 20. The second electrode 22 has a porous configuration in which a large number of through-holes 15 are formed on a matrix 23 made of, for example, a rectangular metal plate. The matrix 23 comprises a first surface 23 a, and a second surface 23 b facing and substantially parallel to the first surface 23 a. The first surface 23 a faces the porous membrane 24. The second surface 23 b faces the cathode chamber 18.

The continuous porous membrane 24 is formed on the first surface 21 a of the first electrode 20 and covers the whole first surface 21 a and the through holes 13. In the present embodiment, the porous membrane 24 is formed in a rectangular shape so as to have dimensions substantially equal to those of the first electrode 20. The porous membrane 24 is interposed between the first surface 21 a of the first electrode 20 and the first surface 23 a of the second electrode 22. The second electrode 22 may not come into direct contact with the porous membrane 24. Alternatively, another structure may be provided between the second electrode 22 and the porous membrane 24.

As the porous membrane 24, a uniform inorganic oxide porous membrane containing an inorganic oxide which is chemically stable is used. Various materials may be used for the inorganic oxide. For example, titanium oxide, silicon oxide, aluminum oxide, niobium oxide, zirconium oxide, tantalum oxide, nickel oxide, tungsten oxide, zircon or zeolite may be used. Of these materials, titanium oxide, zirconium oxide, silicon oxide and aluminum oxide are preferably used. Hydroxide, alkoxide, oxyhalide or hydrate may be contained in the inorganic oxide. When the inorganic oxide is prepared by the hydrolysis of metal halide or metal alkoxide, a composite thereof may be easily obtained depending on the temperature of the subsequent treatment.

When using the first electrode 20 for the anode, titanium oxide, aluminum oxide, zirconium oxide and zircon are preferable as the inorganic oxide for the porous membrane 24, since these materials easily have a positive zeta potential in an acidic region and therefore exhibit an anion-exchange function. When using the first electrode 20 for the cathode, titanium oxide, aluminum oxide, zirconium oxide, silicon oxide, tungsten oxide, zircon and zeolite are preferable as the inorganic oxide for the porous membrane 24, since these materials easily have a negative zeta potential in an alkaline region and therefore exhibit a cation-exchange function.

As schematically shown in FIG. 3D, the porous membrane 24 containing an inorganic oxide may be formed to have irregular pores in a plane and in a three-dimensional manner through application of nanoparticles or sol-gel. In this case, the porous membrane 24 is resistant to bending, etc. The porous membrane 24 may contain polymers in addition to the inorganic oxide. Polymers add flexibility to the membrane. As the polymers, a halogen atom may be preferably substituted on a main chain which is chemically stable. For example, polyvinylidene chloride, polyvinylidene fluoride and Teflon (registered trademark) are preferable. Of these materials, Teflon is particularly preferable. Apart from these materials, as the polymers, polyethylene and an engineering plastics such as polyimide or polyphenylenesulfide may be employed.

As shown in FIG. 3A, the pore dimension of the porous membrane 24 may be formed such that the opening dimension on the first electrode 20 side is different from that on the second electrode 22 side. When the opening dimension of each pore on the second electrode 22 side is made greater than that on the first electrode 20 side, ion transfer can be further facilitated, and moreover, the concentration of stress applied by the through-hole 13 of the first electrode 20 can be reduced. The structure in which the opening dimension on the second electrode 22 side is great facilitates ion transfer caused by diffusion. When the first electrode 20 is used for the anode, a positive potential is applied. Therefore, even when the opening dimension on the first electrode 20 side is less, anions are easily drawn to the first electrode 20. If the pore dimension on the first electrode 20 side is great, the produced chlorine or hypochlorous acid is easily diffused to the porous membrane 24 side.

The pore dimension on the surface of the porous membrane 24 can be measured by a high-resolution scanning electron microscope (SEM). The pores inside the porous membrane can be measured by cross-sectional SEM observation.

As schematically shown in FIG. 3B, the porous membrane 24 comprises a first area 24 a which covers the portion of the first surface 21 a of the first electrode 20, and a second area 24 b which covers the opening of the through-hole 13. Normally, it is difficult to discharge gas such as the produced chlorine in the portion of the first surface 21 a of the first electrode 20. Thus, the electrode unit 12 is easily degraded. To solve this problem, as described above, the pores on the surface of the first area 24 a may be eliminated, in other words, no pore may be formed. Alternatively, the dimension of each pore on the surface of the first area 24 a may be made less than that on the second area 24 b. This structure inhibits an electrolytic reaction in an area which is in contact with the first area 24 a. Thus, the degradation of the electrode unit 12 can be prevented. To form the first area 24 a so as to have no pore, or to reduce the pore dimension, as shown in FIG. 3B, a thin imperforate membrane 29 a or a porous membrane 29 b having a less pore-dimension may be formed on the first surface 21 a of the first electrode 20 by screen printing, etc. It should be noted that, in this case, the reactive area of the first electrode 20 is small. Therefore, it is necessary to cause a sufficient reaction in an electrode area where gas is easily discharged. A side reaction can be reduced by covering the surface (second surface 21 b) opposite to the porous membrane 24 of the first electrode 20 with an electrical insulating membrane.

As shown in FIG. 3C, for the porous membrane 24, a multilayer film including a plurality of porous membranes 28 a and 28 b having different pore-dimensions may be used. In this case, the pore dimension of the porous membrane 28 b located on the second electrode 22 side may be made greater than that of the porous membrane 28 a located on the first electrode 20 side. This structure can further facilitate ion transfer and reduce the concentration of stress applied by the through-hole of the electrode.

The first electrode 20, the porous membrane 24 and the second electrode 22 having the above structures are brought into contact with each other by pressing them in a state where the porous membrane 24 is interposed between the first electrode 20 and the second electrode 22. In this manner, the electrode unit 12 is obtained.

As shown in FIG. 1, the electrode unit 12 is provided in the electrolytic cell 11 and is attached to the dividing wall 14. The electrolytic cell 11 is divided into the anode chamber 16 and the cathode chamber 18 by the dividing wall 14 and the electrode unit 12. Thus, the electrode unit 12 is provided in the electrolytic cell 11 such that the alignment direction of the structural members is, for example, the horizontal direction. The first electrode 20 of the electrode unit 12 faces the anode chamber 16. The second electrode 22 faces the cathode chamber 18.

In the electrolytic device 10, the two poles of the power supply 30 are electrically connected to the first electrode 20 and the second electrode 22. The power supply 30 applies voltage to the first and second electrodes 20 and 22 under control of the control device 36. The voltmeter 34 is electrically connected to the first electrode 20 and the second electrode 22 and detects the voltage applied to the electrode unit 12. The detected data is supplied to the control device 36. The ammeter 32 is connected to the voltage application circuit of the electrode unit 12 and detects the current flowing in the electrode unit 12. The detected data is supplied to the control device 36. The control device 36 controls the application of voltage or load for the electrode unit 12 by the power supply 30 based on the detected data in accordance with the program stored in the memory. The electrolytic device 10 applies voltage or load between the first electrode 20 and the second electrode 22 in a state where the substance for reaction is supplied to the anode chamber 16 and the cathode chamber 18. In this manner, the electrochemical reaction for electrolysis is advanced. The electrolytic device 10 of the present embodiment preferably electrolyzes an electrolyte containing chloride ions.

According to the electrolytic device and the electrode unit having the above structure, the porous membrane 24 containing an inorganic oxide which is chemically stable is formed to cover the first surface of the first electrode 20 and the through-holes. With this structure, the distance between the first electrode 20 and the second electrode 22 can be maintained as constant as possible. Thus, the flow of liquid can be uniform. The electrolytic reaction can occur uniformly at the interfaces between electrodes. Because of the uniform electrolytic reaction, the catalysts and the electrode metals deteriorate uniformly. In addition, an inorganic oxide which is chemically stable is used. Thus, the life duration of the electrode unit can be significantly prolonged. Since the electrolytic reaction occurs uniformly, the reaction efficiency of the electrolytic device can be improved, and further, the deterioration of the electrodes can be inhibited.

In the first electrode 20 having a porous configuration, the through-holes are formed with a tapered or curved surface which enlarges towards the first surface side. With this structure, the contact angle between the opening of each through-hole and the porous membrane 24 is made as an obtuse angle, thereby reducing the concentration of stress on the porous membrane 24.

With the above structures, it is possible to obtain a long-life electrode unit which can maintain the electrolytic performance for a long time, and an electrolytic device comprising the electrode unit.

In the first embodiment, the second electrode 22 has a porous configuration with a large number of through-holes. However, the second electrode 22 is not limited to this configuration. For example, a plate-like electrode without a through-hole may be employed.

FIG. 4 shows the electrode unit according to a first modification example. As shown in this figure, the electrode unit 12 may comprise a diaphragm 26 which transmits at least one of ions and liquid. For example, the diaphragm 26 is formed in a rectangular shape so as to have dimensions substantially equal to those of the first electrode 20, and is interposed between the porous membrane 24 and the first surface 23 a of the second electrode 22. The diaphragm 26 adheres tightly to the porous membrane 24, and further adheres tightly to the whole first surface 23 a of the second electrode 22.

For the diaphragm 26, various electrolyte membranes and porous membranes having nano-pores may be used. A usable example of the electrolyte membranes is a polyelectrolyte membrane such as a cation-exchange solid polyelectrolyte membrane, more specifically, a cation-exchange membrane, or an anion-exchange membrane, or a hydrocarbon-series membrane. Usable examples of the cation-exchange membrane are Nafion (registered trademark of E. I. du Pont de Nemours and Company) 112, 115 and 117, Flemion (registered trademark of Asahi Glass Co., Ltd.), Aciplex (registered trademark of Asahi Glass Co., Ltd.), and GORE-SELECT (registered trademark of W.L. Gore & Associates, Inc.). A usable example of the anion-exchange membrane is A201 manufactured by Tokuyama Corporation. Usable examples of the porous membranes having nano-pores are porous ceramic such as porous glass, porous alumina, porous titania and porous zeolite, and porous polymers such as porous polyethylen, porous propylene and porous teflon. With the diaphragm 26 described above, the ion selectivity can be improved.

FIG. 5 shows a part of the electrode unit according to a second modification example. As shown in FIG. 5(a) and FIG. 5(b), the porous membrane 24 of the electrode unit 12 may be present on the wall surface defining the through-holes 15 of the first electrode 20 (in other words, on the sidewall surface of the through-holes). In other words, the porous membrane 24 may be formed so as to cover the first surface 21 a of the first electrode 20 and a part of or the entire part of the wall surface of at least one through-hole 15. When the porous membrane 24 is formed in this manner, the bond between the first electrode 20 and the porous membrane 24 is strengthened. The porous membrane 24 is difficult to remove even with a thermal cycle, etc.

Now, this specification explains an electrode unit and an electrolytic device according to another embodiment. Note that in the other embodiments described below, the same referential numbers and symbols are given to the same structural elements as the above first embodiment, and the detailed explanations thereof are omitted. The elements different from those of the first embodiment are mainly discussed in detail.

Second Embodiment

FIG. 6 is a cross-sectional view schematically showing an electrolytic device according to a second embodiment. FIG. 7 is an exploded perspective view of an electrode unit. FIG. 8 is a cross-sectional view of the electrode unit. In the second embodiment, a first electrode 20 of an electrode unit 12 has a porous configuration, and through-holes are formed such that the opening dimension on the first surface 21 a side differs from that on the second surface 21 b side.

As shown in FIG. 6 to FIG. 8, the first electrode 20 has a porous configuration in which a large number of through-holes are formed on a matrix 21 made of, for example, a rectangular metal plate. The matrix 21 comprises the first surface 21 a, and the second surface 21 b facing and substantially parallel to the first surface 21 a. The interval between the first surface 21 a and the second surface 21 b, in other words, the thickness of the plate, is defined as T1. The first surface 21 a faces a porous membrane 24. The second surface 21 b faces an anode chamber 16.

A plurality of first holes 40 are formed on the first surface 21 a of the matrix 21 and open on the first surface 21 a. Moreover, a plurality of second holes 42 are formed on the second surface 21 b and open on the second surface 21 b. Each first hole 40 communicates with the second hole 42 facing the first hole 40. Thus, a through-hole penetrating the matrix 21 is formed. The first holes 40 made on the porous membrane 24 side have an opening dimension (R1) which is less than the opening dimension (R2) of the second holes 42. Further, the first holes 40 are greater in number than the second holes 42. The opening area of the second holes 42 is greater than that of the first holes 40. The depth of the first holes 40 is T2, and the depth of the second holes 42 is T3. The holes are formed such that T2+T3=T1. In the present embodiment, the holes are formed such that T2<T3.

The second holes 42 are formed in, for example, a rectangular shape and are arranged in a matrix on the second surface 21 b. The circumferential wall which defines each second hole 42 may be formed to have a tapered surface 42 a or a curved surface so that the dimension enlarges from the bottom of the hole to the opening, in other words, to the second surface side. The interval between adjacent second holes 42, that is, the width of a linear portion of the electrode, is set to W2. Note that the second holes 42 are not limited to a rectangular shape, and may take various other forms. Moreover, the second holes 42 need not be aligned regularly and may be arranged randomly.

The first holes 40 are formed in, for example, a rectangular shape and are arranged in a matrix on the first surface 21 a. The circumferential wall which defines each first hole 40 may be formed to have a tapered or curved surface so that the dimension enlarges from the bottom of the hole to the opening, in other words, to the first surface 21 a. In this embodiment, a plurality of, for example, nine first holes 40 are provided to face one second hole 42. The nine first holes 40 communicate with the second hole 42 and form the through-holes penetrating the matrix 21 together with the second hole 42. Interval W1 between adjacent first holes 40 is set so as to be less than interval W2 between second holes 42. With this structure, the number density of the first holes 40 on the first surface 21 a is sufficiently greater than that of the second holes 42 on the second surface 21 b. Other elements such as the matrix 21 and the catalytic layer of the first electrode 20 have the same structures as the first embodiment.

The opening dimension of the first holes 40 is preferably less in order to make the pressure uniform. However, the first holes 40 need to be large to the extent that substance diffusion can be prevented. In the case of a square, the dimension of each side of the opening is preferably 0.1 to 2 mm, and is more preferably 0.3 to 1 mm. The opening may take a variety of forms such as a square, a rectangle, a rhomboid, a circle and an ellipse, while the opening area is preferably 0.01 to 4 mm² in the same manner as the above square. The opening area is more preferably 0.1 to 1.5 mm². The opening area is further preferably 0.2 to 1 mm². The ratio of the opening area to the electrode area including the opening (in other words, the opening ratio) is preferably 0.05 to 0.5, and is more preferably 0.1 to 0.4, and is further preferably 0.15 to 0.3. If the opening ratio is excessively less, outgassing is difficult. If the opening ratio is excessively great, electrode reaction is inhibited.

Note that the first holes 40 are not limited to a rectangular shape, and may take other forms. Moreover, the first holes 40 need not be aligned regularly and may be arranged randomly. Furthermore, all the first holes 40 may not necessarily communicate with the second holes 42. Some first holes 40 may not communicate with second holes 42. Thus, some first holes 40 may not communicate with the anode chamber 16. For example, the first holes 40 may be formed in a rectangular shape extending from the vicinity of one end of the electrode to the vicinity of the other end of the electrode. In these first holes 40, a plurality of opening portions communicating with the second holes 42 may be arranged at intervals. Only a part of each first hole 40 may communicate with the second holes. The first holes which do not communicate with the second holes can increase the electrode area.

Preferably, 85% or more of all of the first holes 40 have an opening area of 0.01 to 4 mm². More preferably, 90% or more, and further preferably, 95% ore more of all of the first holes 40 have an opening area of 0.01 to 4 mm².

Various shapes may be employed for each second hole 42, such as a square, a rectangle, a rhomboid, a circle or an ellipse. The opening dimension of each second hole 42 is preferably great in order to facilitate outgassing. However, if the opening dimension is great, the electrical resistance is increased. Therefore, the second holes 42 cannot be significantly enlarged. In the case of a square, the dimension of each side of the opening is preferably 1 to 40 mm, and is more preferably 2 to 20 mm. The opening may take a variety of forms such as a square, a rectangle, a rhomboid, a circle and an ellipse, while the opening area is preferably 1 to 1600 mm² in the same manner as the above square. The opening area of the second holes 42 is more preferably 4 to 900 mm², and is further preferably 9 to 400 mm². For example, the opening may be shaped in a rectangle or an ellipse which is long in one direction so as to connect an end and the other end of the electrode.

The porous membrane 24 containing an inorganic oxide is formed on the first surface 21 a of the first electrode 20 so as to cover the whole first surface 21 a and the first holes 40. The porous membrane 24 employs the same porous membrane as the first embodiment described above.

In the second embodiment, as shown in FIG. 6 to FIG. 8, a second electrode (counterelectrode) 22 is structured in the same manner as the first electrode 20. The second electrode 22 has a porous configuration in which a large number of through-holes are formed on a matrix 23 made of, for example, a rectangular metal plate. The matrix 23 comprises a first surface 23 a, and a second surface 23 b facing and substantially parallel to the first surface 23 a. The first surface 23 a faces a diaphragm 26. The second surface 23 b faces a cathode chamber 18.

A plurality of first holes 44 are formed on the first surface 23 a of the matrix 23 and open on the first surface 23 a. Further, a plurality of second holes 46 are formed on the second surface 23 b and open on the second surface 23 b. The opening dimension of the first holes 44 made on the diaphragm 26 side is less than that of the second holes 46. Further, the first holes 44 are greater in number than the second holes 46. The depth of the first holes 44 is less than that of the second holes 46.

A plurality of, for example, nine first holes 44 are provided to face one second hole 46. The nine first holes 44 communicate with the second hole 46 and form the through-holes penetrating the matrix 23 together with the second hole 46. The interval between adjacent first holes 44 is set so as to be less than the interval between the second holes 46. With this structure, the number density of the first holes 44 on the first surface 23 a is sufficiently greater than that of the second holes 46 on the second surface 23 b.

The first electrode 20, the porous membrane 24 and the second electrode 22 having the above structures are brought into contact with each other by pressing them in a state where the porous membrane 24 is interposed between the first electrode 20 and the second electrode 22. In this manner, the electrode unit 12 is obtained. In the present embodiment, an electrolytic device 10 preferably electrolyzes an electrolyte containing chloride ions.

This specification explains an example of a method of manufacturing the first electrode 20 and the porous membrane 24 having the above structures. The first electrode 20 can be manufactured by, for example, an etching method using a mask. As shown in FIG. 9(a) and FIG. 9(b), the flat matrix 21 is prepared. Resist films 50 a and 50 b are applied to the first and second surfaces 21 a and 21 b of the matrix 21. As shown in FIG. 9(c), the resist films 50 a and 50 b are exposed, using an optical mask (not shown). Thus, masks 52 a and 52 b for etching are prepared. As shown in FIG. 9(d), wet etching is applied to the first and second surfaces 21 a and 21 b of the matrix 21 via the masks 52 a and 52 b with solution. In this manner, a plurality of first holes 40 and a plurality of second holes 42 are formed. Subsequently, the first electrode 20 is obtained by removing the masks 52 a and 52 b.

The shape of the tapered or curved surface of the first and second holes 40 and 42 can be controlled based on the material of the matrix 21 and etching conditions. The depth of the first holes 40 is T2, and the depth of the second holes 42 is T3. As stated above, the first and second holes are formed such that T2<T3. In etching, both surfaces of the matrix 21 may be etched at the same time, or may be etched separately. The type of etching is not limited to wet etching. For example, dry etching may be employed. Apart from etching, the first electrode 20 may be manufactured by, for example, an expanding method, a punching method or a processing method using a laser or precision cutting.

Subsequently, the porous membrane 24 is formed on the first surface 21 a of the first electrode 20. As shown in FIG. 9(e), a preprocessing film 24 c is manufactured by applying a solution containing inorganic oxide particles and/or inorganic oxide precursors to the first surface 21 a. Subsequently, as shown in FIG. 9(f), the preprocessing film 24 c is subjected to sintering to manufacture the porous membrane 24 having a large number of pores.

For example, the solution containing inorganic oxide precursors is prepared by dissolving metal alkoxide in alcohol, adding a solvent having a high boiling point such as glycerin to achieve a porous configuration, or blending an organic substance such as fatty acid which is easily oxidized to be carbon dioxide at the time of sintering. To cover the pores of the electrode, the viscosity of the solution is preferably increased by adding a small amount of water and partially hydrolyzing metal alkoxide. Alternatively, a dispersion liquid containing inorganic oxide particles may be applied. Alternatively, they may be combined with each other.

As a method of applying the solution containing inorganic oxide particles and/or inorganic oxide precursors, for example, brush or spray application is preferable, as it is simple and easy. In the process for applying sintering to the preprocessing film 24 c and preparing pores, the sintering temperature is preferably 150 to 600° C.

In the above process for manufacturing the porous membrane 24, as shown in FIG. 10(a), the first and second holes 40 and 42 of the first electrode 20 may be covered by an organic substance 55 before preparing the preprocessing film. Subsequently, the preprocessing film 24 c may be formed on the first surface 21 a of the first electrode 20 as shown in FIG. 10(b). Subsequently, as shown in FIG. 10(c), the organic substance 55 is removed, and the preprocessing film 24 c is burned. Thus, the porous membrane 24 is formed. Alternatively, the preprocessing film 24 c may be burned while the organic substance 55 is left.

In the above manufacturing process, the through-holes of the electrode can be covered certainly when the solution containing inorganic oxide particles and/or inorganic oxide precursors is applied. Further, the film thickness of the inorganic oxide can be made constant such that the film can be flat.

In the second embodiment, the other structures of the electrode unit 12 and the electrolytic device 10 are the same as those of the first embodiment described above. According to the second embodiment, in a manner similar to that of the first embodiment, it is possible to obtain a long-life electrode unit which can maintain the electrolytic performance for a long time, an electrolytic device comprising the electrode unit, and a method of manufacturing an electrode.

According to the second embodiment, in the first electrode 20, the dimension of the first holes 40 formed on the first surface 21 a on the porous membrane 24 side is made less than that of the second holes 42. The number density of the first holes 40 is made great. This structure allows the reduction in the concentration of stress applied from the first electrode 20 side to the porous membrane 24. As a continuous membrane, the porous membrane 24 is brought into contact with the whole first surface 21 a of the first electrode 20. Thus, the holes of the first electrode 20 are covered by the porous membrane 24. The distance between the first electrode 20 and the diaphragm 26 can be easily maintained equally over the whole surface. In this manner, it is possible to prevent occurrence of distribution in the film thickness of the porous membrane 24 and maintain the film thickness of the porous membrane 24 equally. This structure enables the electrolytic reaction to be caused uniformly, thereby improving the reaction efficiency of the electrolytic device and preventing the degradation of the electrolyte membrane.

FIG. 11 shows the electrode unit according to a third modification example. As shown in this figure, in the above second embodiment, the electrode unit 12 may comprise the diaphragm 26 which transmits at least one of ions and liquid. For example, the diaphragm 26 is formed in a rectangular shape so as to have dimensions substantially equal to those of the first electrode 20, and is interposed between the porous membrane 24 and the first surface 23 a of the second electrode 22. The diaphragm 26 adheres tightly to the porous membrane 24, and further adheres tightly to the whole first surface 23 a of the second electrode 22. As the diaphragm 26, a diaphragm similar to that of the first modification example may be used.

Third Embodiment

FIG. 12 is a cross-sectional view showing an electrolytic device according to a third embodiment. In the third embodiment, an electrolytic cell 11 of an electrolytic device 10 is structured as a one-chamber electrolytic cell comprising only one electrolytic chamber 17. An electrode unit 12 is provided in the electrolytic chamber 17. For example, a pipe or a pump for supplying an electrolyte from outside or discharging an electrolyte may be connected to the electrolytic chamber 17.

In the one-chamber electrolytic cell 11, a second electrode (counterelectrode) 22 of the electrode unit 12 preferably has a porous configuration in a manner similar to that of the first electrode 20. The porous configuration enables the electrode area to be increased.

Fourth Embodiment

FIG. 13 is a cross-sectional view showing an electrolytic device according to a fourth embodiment.

As shown in FIG. 13, an electrolytic device 10 comprises a three-chamber electrolytic cell 11 and an electrode unit 12. The electrolytic cell 11 is formed in the shape of a flat and rectangular box. The electrolytic cell 11 is divided into three chambers, specifically, an anode chamber 16, a cathode chamber 18 and an intermediate chamber 19 formed between the electrodes, by a dividing wall 14 and the electrode unit 12.

The electrode unit 12 comprises a first electrode (anode) 20 located in the anode chamber 16, a second electrode (a counterelectrode, a cathode) 22 located in the cathode chamber 18, a porous membrane 24 formed on a first surface 21 a of the first electrode 20, and a porous membrane 27 formed on a first surface 23 a of the second electrode 22. The first electrode 20 and the second electrode 22 face each other across an intervening space such that they are parallel to each other. The intermediate chamber (electrolyte chamber) 19 which stores an electrolyte is formed between the porous membranes 24 and 27 of the first and second electrodes 20 and 22. A holder 25 which holds an electrolyte may be provided in the intermediate chamber 19. The first and second electrodes 20 and 22 may be connected to each other by a plurality of insulating bridges 60.

The electrolytic device 10 comprises a power supply 30 which applies voltage to the first and second electrodes 20 and 22 of the electrode unit 12, an ammeter 32, a voltmeter 34 and a control device 36 which controls these elements. A flow channel for liquid may be provided in the anode chamber 16 and the cathode chamber 18. For example, a pipe or a pump for supplying liquid from outside or discharging liquid may be connected to the anode chamber 16 and the cathode chamber 18. A porous spacer may be provided between the electrode unit 12 and the anode chamber 16 or the cathode chamber 18 depending on the case.

In the electrode unit 12, the first and second electrodes 20 and 22 are formed to have a porous configuration similar to that of the second embodiment. The continuous porous membrane 24 is formed in, for example, a rectangular shape so as to have dimensions substantially equal to those of the first electrode 20, and faces the whole first surface 21 a. The continuous porous membrane 27 is formed in, for example, a rectangular shape so as to have dimensions substantially equal to those of the second electrode 22, and faces the whole first surface 23 a. As these porous membranes 24 and 27, porous membranes similar to those of the first embodiment may be used. Various materials may be used for the porous membranes 24 and 27.

The porous membranes 24 and 27 may also function as diaphragms as long as they are inorganic oxide films having irregular pores in a plane or in a three-dimensional manner. The porous membranes 24 and 27 may be multilayer films of a plurality of porous membranes having different pore-dimensions.

In the fourth embodiment having the above structures, effects similar to those of the first embodiment can be obtained. It is possible to obtain a long-life electrode unit and electrolytic device having a high reaction efficiency.

FIG. 14 shows the electrode unit according to a fourth modification example. As shown in this figure, the electrode unit 12 may comprise diaphragms 26 a and 26 b which transmit at least one of ions and liquid. The diaphragm 26 a is formed in, for example, a rectangular shape so as to have dimensions substantially equal to those of the first electrode 20, and faces the first surface 21 a of the first electrode 20. The porous membrane 24 is interposed between the first surface 21 a of the first electrode 20 and the diaphragm 26 a, and adheres tightly to the first electrode 20 and the diaphragm 26 a.

The diaphragm 26 b is formed in, for example, a rectangular shape so as to have dimensions substantially equal to those of the second electrode 22, and faces the first surface 23 a of the second electrode 22. The porous membrane 27 is interposed between the first surface 23 a of the second electrode 22 and the diaphragm 26 b, and adheres tightly to the second electrode 22 and the diaphragm 26 b.

For the diaphragms 26 a and 26 b, various electrolyte membranes and porous membranes having nano-pores may be used. A usable example of the electrolyte membranes is a polyelectrolyte membrane such as a cation-exchange solid polyelectrolyte membrane, more specifically, a cation-exchange membrane, or an anion-exchange membrane, or a hydrocarbon-series membrane. Usable examples of the cation-exchange membrane are Nafion (registered trademark of E. I. du Pont de Nemours and Company) 112, 115 and 117, Flemion (registered trademark of Asahi Glass Co., Ltd.), Aciplex (registered trademark of Asahi Glass Co.,

Ltd.), and GORE-SELECT (registered trademark of W. L. Gore & Associates, Inc.). A usable example of the anion-exchange membrane is A201 manufactured by Tokuyama Corporation. Usable examples of the porous membranes having nano-pores are porous ceramic such as porous glass, porous alumina and porous titanium, and porous polymers such as porous polyethylene, porous propylene and porous teflon.

Now, various examples and comparative examples are described.

EXAMPLE 1

For the electrode matrix 21, a flat titanium plate having a plate thickness (T1) of 0.5 mm is employed. This titanium plate is etched as shown in FIG. 9. In this manner, the electrode 20 shown in FIG. 6 and FIG. 7 is manufactured. In the electrode, the thickness (T2) of the area including the small first holes 40 (in other words, the depth of the first holes) is 0.15 mm. The thickness (T3) of the area including the large second holes 42 (in other words, the depth of the second holes) is 0.35 mm. Each first hole 40 has a square shape. The dimension (R1) of each side is 0.57 mm. Each second hole 42 has a square shape. While the vertexes of the square are rounded, the dimension (R2) of each side of the square which can be obtained by extrapolating the linear potion is 2 mm. The width (W1) of the linear portion formed between adjacent first holes 40 is 0.1 mm. The width (W2) of the broad linear portion formed between adjacent second holes 42 is 1.0 mm.

This etched electrode matrix 21 is processed in 10 wt % of an oxalic acid solution at 80° C. for an hour. A solution adjusted by adding 1-butanol to iridium chloride (IrCl3.nH2O) so as to obtain 0.25M (Ir) is applied to the first surface 21 a of the electrode matrix 21. Subsequently, drying and burning are applied. In this case, drying is performed at 80° C. for 10 minutes, and burning is performed at 450° C. for 10 minutes. The above application, drying and burning are repeated five times. The electrode matrix made through this process is cut out such that the reactive electrode area can be 3 cm×4 cm. In this manner, the first electrode (anode) 20 is manufactured.

Ethanol and diethanolamine are added to titanium (IV) tetraisopropoxide under ice bath. An aqueous solution of ethanol is added drop by drop while stirring it. Thus, sol is prepared. The thin film is made porous by thermal processing. Polyethylene glycol (molecular weight: 5000) for increasing the viscosity of the sol is added to the sol cooled to a room temperature. The first surface 21 a of the electrode 20 is coated with a brush. The coated film is burned at 500° C. for 7 minutes. Coating and burning are repeated at three times. Subsequently, burning is performed at 500° C. for an hour. Thus, the porous membrane 24 formed of titanium oxide is obtained.

In the above process for manufacturing the electrode, instead of preparing iridium oxide, platinum is sputtered to obtain the second electrode (the counterelectrode, the cathode) 22. In the same way as above, the porous membrane 27 formed by a titanium oxide film is prepared on the second electrode 22.

The electrode unit 12 shown in FIG. 13 is manufactured, using the above first and second electrodes 20 and 22. As the holder 25 which holds the electrolyte, porous polystyrene having a thickness of 5 mm is used. The first and second electrodes, the porous membranes, the dividing wall and the porous polystyrene are laid to overlap each other and are secured by a silicone sealant and screws. In this manner, the electrode unit 12 is obtained. The electrolyte device 10 shown in FIG. 13 is manufactured, using this electrode unit 12.

The anode and cathode chambers 16 and 18 of the electrolytic cell 11 are each formed from a vinyl-chloride container in which a straight flow channel is formed. The control device 36, the power supply 30, the voltmeter 34 and the ammeter 32 are provided. A pipe and a pump for supplying water to the anode and cathode chambers 16 and 18 are connected to the electrolytic cell 11. Further, a saturated salt water tank, a pipe and a pump for circulating a saturated salt water to the holder (porous polystyrene) 25 of the electrode unit 12 are connected to the electrode unit.

The electrolytic device 10 is operated for electrolysis at a voltage of 4 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 2

The electrolytic device 10 is manufactured in the same manner as in Example 1 except that A201 of Tokuyama Corporation, which is an anion-exchange membrane, is employed as the diaphragm 26 a, and Nafion 117 is provided as the diaphragm 26 b between the porous membrane 24 or 27 and the holder 25 which holds an electrolyte.

The electrolytic device 10 is operated for electrolysis at a voltage of 5.2 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. In Example 2, the concentration of sodium chloride contained in the aqueous hypochlorous acid is decreased in comparison with Example 1. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, the electrolytic treatment is stable.

EXAMPLE 3

The electrolytic device 10 is manufactured in the same manner as in Example 1 except that tetraethoxysilane is employed instead of titanium (IV) tetraisopropoxide.

This electrolytic device is operated for electrolysis at a voltage of 4.3 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 4

The electrolytic device 10 is manufactured in the same manner as in Example 1 except that aluminum triisopropoxide is employed instead of titanium (IV) tetraisopropoxide.

This electrolytic device is operated for electrolysis at a voltage of 4.0 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 5

The electrolytic device 10 is manufactured in the same manner as in Example 1 except that zirconium (IV) tetraisopropoxide is employed instead of titanium (IV) tetraisopropoxide.

This electrolytic device is operated for electrolysis at a voltage of 4.2 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 6

The first and second electrodes are manufactured in the same manner as in Example 1. In the same manner as in Example 1, the porous membrane 24 formed of titanium oxide is prepared on the first electrode 20. They are laid to overlap each other, using a silicone sealant and screws. Thus, the electrode unit 12 is obtained.

The electrolytic device 10 shown in FIG. 12 is manufactured, using this electrode unit 12. The control device 36, the power supply 30, the voltmeter 34 and the ammeter 32 are provided. A pipe and a pump for supplying a salt water to the electrolytic chamber 17 are provided. The electrolytic device 10 is operated for electrolysis at a voltage of 3.7 V and a current of 1.5 A. Thus, a sodium hypochlorite solution is produced. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 7

The first and second electrodes 20 and 22 are manufactured in the same manner as in Example 1. Spin coating is applied to the second surface 21 b of the first electrode 20 with an ethyl acetate solution of PMMA to fill the second holes 42 and 46 of the electrode with PMMA. An aqueous dispersion containing titanium oxide nanoparticles having a grain size of 50 nm is applied to the first surface 21 a of the first electrode 20 by screen printing. After provisional sintering at 100° C., the PMMA is removed by ethyl acetate. Subsequently, burning is performed at 450° C. Then, the electrode is put into water. Titanium tetrachloride is added drop by drop. After the electrode is left at room temperature for five hours, it is rinsed in water and burned at 450° C. Thus, the porous membrane 24 formed of titanium oxide is obtained.

In the above process for manufacturing the electrode, instead of preparing iridium oxide, platinum is sputtered to obtain the second electrode (cathode) 22. In the same way as above, the porous membrane 27 formed by a titanium oxide film is prepared on the second electrode 22.

The electrode unit 12 shown in FIG. 13 is manufactured, using the above first and second electrodes 20 and 22. As the holder 25 which holds the electrolyte, porous polystyrene having a thickness of 5 mm is used. The first and second electrodes, the porous membranes, the diving wall and the porous polystyrene are laid to overlap each other and are secured by a silicone sealant and screws. In this manner, the electrode unit 12 is obtained. The electrolytic device 10 shown in FIG. 13 is manufactured, using this electrode unit 12.

The anode and cathode chambers 16 and 18 of the electrolytic cell 11 are each formed from a vinyl-chloride container in which a straight flow channel is formed. The control device 36, the power supply 30, the voltmeter 34 and the ammeter 32 are provided. A pipe and a pump for supplying tap water to the anode and cathode chambers 16 and 18 are connected to the electrolytic cell 11. Further, a saturated salt water tank, a pipe and a pump for circulating a saturated salt water to the holder (porous polystyrene) 25 of the electrode unit 12 are connected to the electrode unit.

The electrolytic device 10 is operated for electrolysis at a voltage of 4 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 8

The first and second electrodes are manufactured in the same manner as in Example 1. An aqueous dispersion containing titanium oxide nanoparticles having a grain size of 50 nm is applied to fabric formed of polyvinylidene chloride fibers with a thickness of 200 μm by dip coating and arranged on the first surface of the first electrode. After burning is performed at 150° C., the electrode is put into water. Titanium tetrachloride is added drop by drop. After the electrode is left at room temperature for five hours, it is rinsed in water and burned at 150° C. Thus, the porous membrane 24 containing titanium oxide is obtained.

In the above process for manufacturing the electrode, instead of preparing iridium oxide, platinum is sputtered to obtain the second electrode (cathode) 22. In the same way as above, the porous membrane 27 containing a titanium oxide film is prepared on the second electrode 22.

The electrode unit 12 shown in FIG. 14 is manufactured, using the above first and second electrodes. A201 of Tokuyama Corporation, which is an anion-exchange membrane, is employed as the diaphragm 26 a. Nafion 117 is employed as the diaphragm 26 b. As the holder 25 which holds the electrolyte, porous polystyrene having a thickness of 5 mm is used. They are laid to overlap each other and are bonded together by a silicone sealant and screws. Thus, the electrode unit 12 is obtained. The electrolytic device is manufactured, using this electrode unit 12.

The anode and cathode chambers 16 and 18 of the electrolytic cell 11 are each formed from a vinyl-chloride container in which a straight flow channel is formed. The control device 36, the power supply 30, the voltmeter 34 and the ammeter 32 are provided. A pipe and a pump for supplying tap water to the anode and cathode chambers 16 and 18 are connected to the electrolytic cell 11. Further, a saturated salt water tank, a pipe and a pump for circulating a saturated salt water to the holder (porous polystyrene) 25 of the electrode unit 12 are connected to the electrode unit.

The electrolytic device 10 is operated for electrolysis at a voltage of 5.5 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 9

The first and second electrodes are manufactured in the same manner as in Example 1. A hydrophilic Teflon-coated filter is put into water. Then, titanium tetrachloride is added drop by drop. After the electrode is left at 50° C. for two hours, it is rinsed in water and burned at 250° C. Thus, the porous membrane 24 containing titanium oxide is obtained.

In the above process for manufacturing the electrode, instead of preparing iridium oxide, platinum is sputtered to obtain the second electrode (cathode) 22. In the same way as above, the porous membrane 27 containing titanium oxide is prepared on the second electrode 22.

The electrode unit 12 shown in FIG. 14 is manufactured, using the above first and second electrodes. A201 of Tokuyama Corporation, which is an anion-exchange membrane, is employed as the diaphragm 26 a. Nafion 117 is employed as the diaphragm 26 b. As the holder 25 which holds the electrolyte, porous polystyrene having a thickness of 5 mm is used. They are laid to overlap each other and are bonded together by a silicone sealant and screws. Thus, the electrode unit 12 is obtained. The electrolytic device is manufactured, using this electrode unit 12.

The anode and cathode chambers 16 and 18 of the electrolytic cell 11 are each formed from a vinyl-chloride container in which a straight flow channel is formed. The control device 36, the power supply 30, the voltmeter 34 and the ammeter 32 are provided. A pipe and a pump for supplying tap water to the anode and cathode chambers 16 and 18 are connected to the electrolytic cell 11. Further, a saturated salt water tank, a pipe and a pump for circulating a saturated salt water to the holder (porous polystyrene) 25 of the electrode unit 12 are connected to the electrode unit.

The electrolytic device 10 is operated for electrolysis at a voltage of 5.7 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the first electrode (anode) 20 side, and aqueous sodium hydroxide is produced on the second electrode (cathode) 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

EXAMPLE 10

For the electrode matrix 21, a flat titanium plate having a plate thickness (T1) of 0.5 mm is employed. This titanium plate is etched as shown in FIG. 9. In this manner, an electrode is manufactured. In the electrode, the thickness (T2) of the area including the small first holes 40 (in other words, the depth of the first holes) is 0.15 mm. The thickness (T3) of the area including the large second holes 42 (in other words, the depth of the second holes) is 0.35 mm. The first holes 40 have a rhomboid shape. The dimension of the longer diagonal line is 0.69 mm. The dimension of the shorter diagonal line is 0.4 mm. The second holes 42 have a rhomboid shape. The dimension of the longer diagonal line is 6.1 mm. The dimension of the shorter diagonal line is 3.5 mm. The width (W1) of the linear portion formed between adjacent first holes 40 is 0.15 mm. The width (W2) of the broad linear portion formed between adjacent second holes 42 is 1 mm. The other structures are the same as those of Example 1. On these conditions, the electrode unit 12 and the electrolytic device 10 are manufactured.

The electrolytic device 10 is operated for electrolysis at a voltage of 5.3 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the anode 20 side, and aqueous sodium hydroxide is produced on the cathode 22 side. Even after continuous operation for 1000 hours, no substantial rise in voltage or change in product concentration is observed. Thus, a stable electrolytic treatment can be carried out.

COMPARATIVE EXAMPLE 1

An electrolytic device is manufactured in the same manner as in Example 1 except that a porous polystyrene membrane is employed instead of the continuous inorganic porous membrane. This electrolytic device is operated for electrolysis at a voltage of 4 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the anode side, and aqueous sodium hydroxide is produced on the cathode side. After continuous operation for 1000 hours, a significant rise in voltage and a decrease in product concentration are observed. Thus, it is found that this device lacks a long-term stability.

COMPARATIVE EXAMPLE 2

An electrode unit and an electrolytic device are manufactured in the same manner as in Example 7 without coating with PMMA. In this electrode unit, the through-holes are not covered by an inorganic porous membrane.

This electrolytic device is operated for electrolysis at a voltage of 3.5 V and a current of 1.5 A. Aqueous hypochlorous acid is produced on the anode side, and aqueous sodium hydroxide is produced on the cathode side. A great amount of salt is contained in the aqueous hypochlorous acid.

The present invention is not limited to the embodiments described above but the constituent elements of the invention can be modified in various manners without departing from the spirit and scope of the invention. Various aspects of the invention can also be extracted from any appropriate combination of a plurality of constituent elements disclosed in the embodiments. Some constituent elements may be deleted from all of the constituent elements disclosed in the embodiments. The constituent elements described in different embodiments may be combined arbitrarily.

For example, the first electrode and the second electrode are not limited to rectangular shapes, but various other forms may be selected. The first and second holes of the first electrode are not limited to rectangular shapes, and may have various other shapes such as a circular or elliptical shape. Further, the material of each structural member is not limited to that employed in the embodiments or examples discussed, but various other materials may be selected as needed. The electrolytic cell of the electrolytic device is not limited to one- to three-chamber electrolytic cells, and may be applied to any types of electrolytic cells using electrodes in general. The electrolytes and products are not limited to salt or hypochlorous acid, and may be developed into various electrolytes and products. 

What is claimed is:
 1. An electrode unit comprising: a first electrode comprising a first surface, a second surface located on a side opposite to the first surface, and a plurality of through-holes opening on the first surface and the second surface; a second electrode opposed to the first surface of the first electrode; and a porous membrane containing inorganic oxide, provided on the first surface of the first electrode to cover the first surface and the through-holes.
 2. The electrode unit of claim 1, wherein an opening area of the through-holes on the first surface is 0.01 to 4 mm².
 3. The electrode unit of claim 2, wherein the first electrode comprises a plurality of first holes opening on the first surface, and a plurality of second holes opening on the second surface, the second holes having a dimension greater than a dimension of the first holes, and one second hole communicates with a plurality of first holes to form the through holes.
 4. The electrode unit of claim 3, wherein an opening area of the second holes on the second surface is 1 to 1600 mm².
 5. The electrode unit of claim 3, wherein a number density of the first holes per unit area is greater than a number density of the second holes per unit area.
 6. The electrode unit of claim 3, wherein the first holes have a tapered or curved surface which widens towards the first surface side.
 7. The electrode unit of claim 1, further comprising a diaphragm which is provided between the porous membrane and the second electrode, and transmits at least one of an ion and liquid.
 8. The electrode unit of claim 1, wherein the second electrode has a porous configuration including a plurality of through-holes.
 9. The electrode unit of claim 1, wherein the inorganic oxide of the porous membrane is at least one selected from titanium oxide, aluminum oxide, zirconium oxide and zircon.
 10. The electrode unit of claim 1, wherein the inorganic oxide of the porous membrane is at least one selected from titanium oxide, silicon oxide, aluminum oxide, zirconium oxide, tungsten oxide, zircon and zeolite.
 11. The electrode unit of claim 1, wherein the porous membrane has irregular pores in a plane and in a three-dimensional manner.
 12. The electrode unit of claim 1, wherein the porous membrane is provided such that a pore dimension of a surface on the first electrode side is different from a pore dimension of a surface on the second electrode side.
 13. The electrode unit of claim 1, wherein the porous membrane comprises a first area which is in contact with the first surface of the first electrode, and a second area which covers the through-holes, and an imperforate membrane or a porous membrane having a pore-dimension less than a dimension of a surface pore of the second area is further provided on a surface of the first area.
 14. The electrode unit of claim 1, wherein the porous membrane covers a part of or an entire part of a wall surface defining the through-holes of the first electrode.
 15. The electrode unit of claim 1, wherein a space for inputting an electrolyte, or a holder for holding an electrolyte is provided between the first electrode and the second electrode.
 16. An electrolytic cell comprising: an electrolytic chamber; and the electrode unit of claim 1, provided in the electrolytic chamber.
 17. An electrolytic device comprising: an electrolytic cell comprising an electrolytic chamber; the electrode unit of claim 1, provided in the electrolytic chamber; and a power supply which applies voltage to the first and second electrodes of the electrode unit.
 18. The electrolytic device of claim 17, wherein the electrode unit electrolyzes an electrolyte containing a chloride ion.
 19. A method of manufacturing an electrode used for an electrode unit, the method comprising: forming a plurality of through-holes on an electrode matrix; forming a preprocessing membrane by applying a solution containing at least one of an inorganic oxide particle and a precursor to the electrode matrix; and forming a porous membrane having a large number of pores by burning the preprocessing membrane.
 20. A method of manufacturing an electrode used for an electrode unit, the method comprising: forming a plurality of through-holes on an electrode matrix; applying an organic substance to the through-holes and one of surfaces of the electrode matrix; forming a preprocessing membrane by applying a solution containing at least one of an inorganic oxide particle and a precursor to the other surface of the electrode matrix; and forming a porous membrane having a large number of pores by burning the preprocessing membrane after removing the organic substance or without removing the organic substance. 